As a printing device for printing characters, patterns or the like on a tire surface, a swiveling type tire printer as disclosed in Patent Literature 1 is conventionally known. The swiveling type tire printer has a function of adjusting its center position, height, and turning radius according to the size of the tire fixed to a base, and prints characters and patterns while swiveling above a tire sidewall with a strut extending along the center of the tire as a rotational axis.
However, the tire sidewall is curved rather than flat, so that the position and posture of the printer head described in Patent Literature 1 with respect to the tire surface may differ depending on the position on the sidewall of the tire. In other words, as shown in FIG. 4, the distance between the sidewall of the tire T and a printer head 103 becomes minimum at a maximum width position on the sidewall, and becomes larger as further away from the maximum width position of the sidewall. Therefore, at the position where the distance between the tire side surface T and the printer head 103 becomes excessively large, the ink ejected from the printer head 103 is diffused to make characters, patterns or the like blurry. In addition, since the printer described in Patent Literature 1 swivels the printer head along the sidewall, the radius of swivel and the height of the printer described in Patent Literature 1 need to be adjusted each time when the tire size is changed. The operations thus become complicated.
These problems can be solved by using an ink-jet head to perform the printing on a rotating tire while the sidewall is pressed by a roller to flatten the surface to be printed as described in Patent Literature 2. However, after the printing is performed under a state that the side wall is pressed by a roller to flatten the surface to be printed, and when an internal pressure is applied to the tire and the tire side wall becomes curved (e.g. when the tire is used), the characters and patterns are stretched. As a result, the characters and patterns become distorted which impairs the appearance. In addition, since the sidewall must be pressed evenly by the roller according to the technique described in Patent Literature 2, the operations are complicated.